Ace, Lowes, Home Depot, 'Nard's, etc... Find one that fits. It ain't rocket science.
Naaaah... I'm not that anal. I could care less if it was parked, painted, bare steel, bare brass or chrome plated. It's just a dang cotter pin. You're going to use it once and replace it with a new one after cleaning anyhow. You're talking about a piece of hardware that costs all of about 2 or 3 cents.Soak cotter pins overnight in muratic acid, rinse with water, blast & parkerize!